U.S. patent application number 11/658463 was filed with the patent office on 2009-02-19 for conditional scanning.
This patent application is currently assigned to NOKIA CORPORATION. Invention is credited to Kanji Kerai.
Application Number | 20090046763 11/658463 |
Document ID | / |
Family ID | 32982582 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090046763 |
Kind Code |
A1 |
Kerai; Kanji |
February 19, 2009 |
Conditional Scanning
Abstract
A method of controlling a low power radio receiver including
controlling the radio receiver for a first, relatively short,
period of time to detect radio transmissions in a predetermined
frequency band, and determining whether to control the radio
receiver for a subsequent second relatively longer period of time
to receive data from a subsequent radio transmission in the
predetermined frequency band.
Inventors: |
Kerai; Kanji; (London,
GB) |
Correspondence
Address: |
HARRINGTON & SMITH, PC
4 RESEARCH DRIVE, Suite 202
SHELTON
CT
06484-6212
US
|
Assignee: |
NOKIA CORPORATION
Espoo
FI
|
Family ID: |
32982582 |
Appl. No.: |
11/658463 |
Filed: |
November 8, 2004 |
PCT Filed: |
November 8, 2004 |
PCT NO: |
PCT/GB2004/004717 |
371 Date: |
September 12, 2008 |
Current U.S.
Class: |
375/136 |
Current CPC
Class: |
Y02D 70/142 20180101;
H04W 84/18 20130101; H04W 56/00 20130101; Y02D 70/40 20180101; Y02D
70/144 20180101; Y02D 70/22 20180101; H04B 1/713 20130101; Y02D
30/70 20200801 |
Class at
Publication: |
375/136 |
International
Class: |
H04B 1/713 20060101
H04B001/713 |
Claims
1. A method of controlling a radio receiver comprising: controlling
the radio receiver for a first, relatively short, period of time to
detect radio transmissions in a predetermined frequency band, and
determining whether to control the radio receiver for a subsequent
second relatively longer period of time to receive data from a
subsequent radio transmission in the predetermined frequency
band.
2. A method as claimed in claim 1, wherein controlling the receiver
for a first relatively short period of time involves enabling fast
hopping of a receiving frequency at the receiver over the first
period of time.
3. A method as claimed in claim 2, wherein the predetermined
frequency band comprises a plurality of separate frequency
channels, wherein the fast hopping hops through the plurality of
separate frequency channels at least once during the first period
of time.
4. A method as claimed in claim 2, wherein the subsequent
transmission is a radio packet of predetermined length, wherein the
fast hopping hops through all the channels of the predetermined
frequency band in a period of time corresponding to the
predetermined length.
5. A method as claimed in claim 2, wherein the fast hopping hops at
a rate greater than 1 million hops per second.
6. A method as claimed in claim 1, wherein the subsequent
transmission is a radio packet that is transmitted in a series of
radio packets, wherein the first relatively short period of time is
not less than the maximum duration between the transmission of
adjacent radio packets in the series.
7. A method as claimed in claim 1, wherein the first relatively
short period of time is less than 1 ms.
8. A method as claimed in claim 1, further comprising controlling
the receiver for a subsequent, second relatively long period of
time to receive data from a subsequent radio transmission in the
predetermined frequency band.
9. A method as claimed in claim 1, wherein enabling the receiver
for a subsequent, second relatively long period of time involves
using a slowly hopping receiving frequency at the receiver.
10. A method as claimed in claim 9, wherein the second relatively
long period of time is greater than 10 ms.
11. A method as claimed in claim 9, wherein the receiving frequency
hops more slowly than once per second.
12. A method as claimed in claim 1, wherein the step of controlling
the receiver for a first relatively short period of time to detect
radio transmissions in a predetermined frequency band occurs
periodically at least once every 2.56 s.
13. A method as claimed in claim 1, wherein the step of controlling
the receiver for a first, relatively short, period of time to
detect radio transmissions in a predetermined frequency band
comprises RSSI detection.
14. A method as claimed in claim 1, wherein the transceiver is
unsynchronized to the source of the radio transmission received
during the second period of time.
15. A method as claimed in claim 1, wherein the received data is
used for identifying a received data packet.
16. A method as claimed in claim 15, wherein the received data is
an Access Code.
17. A method as claimed in claim 16, further comprising
identification of the received packet by correlating for the Access
Code.
18. A method as claimed in claim 17, wherein the correlation
establishes synchronization.
19. A method as claimed in claim 1, wherein detecting the radio
transmission in the first relatively short period of time provides
gross frequency and time synchronization that is used to set
initial conditions for the receiver at the beginning of the second
period of time.
20. A method as claimed in claim 1, the receiver is controlled for
a subsequent, second relatively longer period of time to receive
data from a subsequent radio transmission in the predetermined
frequency band if radio transmissions are detected during the first
period of time.
21. A method as claimed in claim 1, the receiver is controlled for
a subsequent, second relatively longer period of time to receive
data from a subsequent radio transmission in the predetermined
frequency band if the transmission or transmissions detected in the
first period of time correspond to a Bluetooth paging or inquiry
procedure.
22. A method as claimed in claim 1, the receiver is not controlled
for a subsequent, second relatively longer period of time to
receive data from a subsequent radio transmission in the
predetermined frequency band if the transmissions detected in the
first period of time correspond to broadband radio
transmissions.
23. A radio receiver device comprising: radio receiver circuitry; a
clock; and control circuitry for controlling the radio receiver
circuitry during a first, relatively short, period of time to
detect radio transmissions in a predetermined frequency band and
for controlling whether the radio receiver circuitry attempts,
during a subsequent second relatively longer period of time, to
receive data from a subsequent radio transmission in the
predetermined frequency band.
24. A chip-set for a radio receiver comprising: control circuitry
for controlling radio receiver circuitry during a first, relatively
short, period of time to detect radio transmissions in a
predetermined frequency band and for controlling whether the radio
receiver circuitry attempts, during a subsequent second relatively
longer period of time, to receive data from a subsequent radio
transmission in the predetermined frequency band.
25. A computer program comprising computer program instructions
which when loaded into a processor provide control circuitry for
controlling radio receiver circuitry during a first, relatively
short, period of time to detect radio transmissions in a
predetermined frequency band and for controlling whether the radio
receiver attempts, during a subsequent second relatively longer
period of time, to receive data from a subsequent radio
transmission in the predetermined frequency band.
26. A record medium embodying the computer program as claimed in
claim 25.
27. A method of controlling a radio receiver comprising:
controlling the radio receiver to perform fast frequency hopping
for a first relatively short period of time to detect radio
transmissions in a predetermined frequency band, and determining
whether to control the radio receiver to receive for a subsequent,
second relatively longer period of time.
28. A method of controlling a radio receiver comprising:
controlling the radio receiver for a first, relatively short,
period of time to detect radio transmissions in a predetermined
frequency band and thereby obtain gross time and frequency
synchronization, and controlling the radio receiver for a
subsequent second relatively longer period of time to receive data
from a subsequent radio transmission in the predetermined frequency
band and thereby obtain exact time and frequency
synchronization.
29. A method of scanning in a low power radio receiver comprising
activating the receiver in a first mode in which the receiver is
periodically switched on for a relatively short period of time to
detect RF activity in a predetermined frequency band, and, in
response to detection of RF activity, activating the receiver in a
second mode in which the receiver is periodically switched on for a
relatively longer period of time to receive RF signals in the
frequency band.
30. (canceled)
31. (canceled)
Description
FIELD OF THE INVENTION
[0001] Embodiments of the present invention relate to conditional
scanning. In particular, they relate to a conditional page scan
and/or a conditional inquiry scan.
BACKGROUND TO THE INVENTION
[0002] FIG. 1 illustrates a piconet 2 which is an ad-hoc wireless
network of Bluetooth devices 4 that can communicate with each other
using radio packets. The piconet 2 has a hub and spoke topology and
is controlled by a Master device 4A at the hub with radio links 6
forming the spokes. Up to seven slave devices 4B can be located on
seven respective spokes. Only one device in the piconet 2 transmits
at a time. Each Slave device 4B can only communicate with the
Master device 4A and the Master device 4A can communicate with any
of the Slaves 4B.
[0003] The radio links 6 are formed using low power radio frequency
transmissions in the 2.4 GHz ISM band. The radio links 6 use fast
frequency-hopping spread-spectrum (FHSS) technique. The frequency
hops at 1600 hops/s in a pseudo-random fashion over 79 one MHz
channels.
[0004] The communication channel used in the piconet 2 is a
Time-Division Duplex radio channel. The channel is divided into a
sequential series of slots of 625 .mu.s duration. The Master 4A
starts transmission in even numbered slots while the Slaves 4B
transmit in odd numbered slots. A transmission is typically a
single packet that occupies a single slot. However, in certain
circumstances the packet may occupy 3 or 5 slots.
[0005] The frequency at which a packet is transmitted is determined
by the piconet's frequency-hopping sequence and the phase within
the sequence at the time of transmission. The piconet's
frequency-hopping sequence is derived from the Bluetooth Device
Address of the Master device 4A. The phase within the
frequency-hopping sequence is determined by the Bluetooth Clock of
the Master device 4A. The frequency hops every 625 .mu.s i.e. every
slot.
[0006] The radio packets transmitted within the piconet 2 use, as a
preamble, an Access Code that is dependent upon the Bluetooth
Device Address of the Master device 4A.
[0007] It will therefore be appreciated that for a connectable
device 4C to join a piconet 2 it must first receive an indication
of the Bluetooth Device Address of the Master device 4A and an
indication of the Bluetooth Clock value of the Master Device 4A.
The Bluetooth Clock value enables the connectable device 4C to
synchronize its timing and frequency hopping to that of the piconet
2. The Bluetooth Address enables the connectable device, when it
joins the piconet 2, to send packets with the correct Access Code,
to use the correct frequency-hopping sequence for the piconet 2 and
to detect the arrival of transmitted packets from the Master 4A and
thereby maintain time and frequency synchronization with the
piconet 2. The Bluetooth Address and Bluetooth Clock value of the
Master device 4A are sent to a connectable device 4C during a
paging procedure.
[0008] The paging procedure for forming connections is asymmetrical
and requires that one Bluetooth device carries out the page
(connection) procedure while the other Bluetooth device is
connectable (page scanning). The procedure is targeted so that the
page procedure is only responded to by one specified Bluetooth
device.
[0009] The connectable device (e.g. 4C) uses a special slow
frequency hopping physical channel to listen for connection request
packets from the paging device (e.g. 4A) which uses a fast
frequency hopping channel. This slow frequency hopping physical
channel has attributes that are specific to the connectable device
4C, hence only a paging device 4A with knowledge of the connectable
device 4C is able to communicate on this channel.
[0010] In the paging procedure, the paging device 4A transmits a
paging request for a target connectable device 4C that is to be
joined to the piconet as a Slave device to the Master paging
device. Each paging request is a packet that has as its preamble an
Access Code that is dependent upon the Bluetooth Device Address of
the target connectable device 4C. The frequency at which the packet
is transmitted is determined from a page frequency-hopping sequence
and the phase within the sequence. The page frequency-hopping
sequence is a sequence of 32 frequencies derived from the Bluetooth
Device Address of the target connectable device 4C. The phase
within the sequence at the time of transmission is determined from
an estimate of the Bluetooth Clock of the target connectable device
4C as emulated in the paging device 4A. As the paging device 4A can
only estimate the Bluetooth clock value of the connectable device
4C, the paging device 4A transmits a series of paging requests each
at a different frequency taken from a train A of the 16 most
probable frequencies within the page frequency-hopping sequence.
Each paging request is an ID packet of size 68 bits (68 us
duration). Two paging requests, at successive frequencies in the
train A, are transmitted in each even numbered slot. Thus a train
of 16 paging requests is transmitted over 10 ms. The train is then
repeated 128 or 256 times. If no reply is received paging requests
are repeatedly transmitted using the remaining train B of 16
frequencies from the page frequency-hopping sequence.
[0011] Each connectable Bluetooth device, that is one that is
available to join a piconet, periodically enters a page scan state
in which it scans for paging requests transmitted for it. During a
scan a sliding correlator correlates against the expected Access
code and triggers when a threshold is exceeded.
[0012] In the page scan state, the Access Code used is derived from
the Bluetooth Address of the connectable device.
[0013] The Bluetooth Specification requires a page scan to be
performed every 1.28 s or 2.56 s. The page scan lasts between 11.25
and 2560 ms. During page scanning, the receiver of the connectable
device 4C attempts sequentially to receive at each one of the
frequencies of the page frequency-hopping sequence frequency. The
phase within the sequence is determined by the Bluetooth Clock of
the connectable device 4C. The receiving frequency typically
changes every 1.28 s.
[0014] The frequency at which a connectable device 4C receives a
page request allows the connectable device to roughly synchronize
in time and frequency with the paging device. The correlation with
the Access code of the paging request provides time
synchronization. The connectable device 4C transmits a reply to the
paging device 4A a predetermined time after receiving the page
request and at a frequency related to the frequency of the received
page request. The connectable device's receiver is then activated a
predetermined time later to receive an FHS packet from the paging
device 4A, which allows the connectable device 4C to join the
piconet 2 as a Slave. The FHS packet comprises the Bluetooth
Address of the Master device 4A and the Bluetooth Clock value of
the Master device 4A.
[0015] It is apparent that if the paging device 4A is to page a
connectable device 4C, then it typically requires the Bluetooth
Device Address of that device and (optionally) the Bluetooth Clock
value of that device. The Bluetooth Device Address enables the
paging device 4A to send packets with the correct Access Code and
to use the correct frequency-hopping sequence. The Bluetooth Clock
value enables the paging device 4A to emulate the timing in the
target connectable device 4C and accurately estimate the most
probably frequency currently being used by the connectable device
4C in page scan mode.
[0016] An Inquiry procedure is typically used by a device to obtain
the Bluetooth Clock values and Bluetooth Device Addresses of the
connectable Bluetooth devices that are within range. It is an
asymmetrical procedure that uses a special physical channel. The
procedure is not targeted so that the inquiry procedure is
responded to by all connectable Bluetooth devices within range.
[0017] The connectable device (e.g. 4C) uses a special slow
frequency hopping physical channel to listen for inquiry packets
from an inquiring device (e.g. 4A) which uses a fast frequency
hopping channel to transmit the inquiry packets. This special slow
frequency hopping physical channel has independent attributes that
are not specific to the inquiring device 4A or the connectable
device 4C.
[0018] In the inquiry procedure, the inquiring device 4C
continually broadcasts an inquiry packet at different hop
frequencies. Each inquiry packet has as its preamble an Inquiry
Access Code. The frequency at which the packet is transmitted is
determined from an inquiry frequency-hopping sequence and the phase
within the sequence at the time of transmission. The inquiry
frequency-hopping sequence is derived from the Inquiry Access Code.
The phase within the sequence at the time of transmission is
determined from the Bluetooth Clock of the inquiring device 4A. The
inquiry frequency-hopping sequence of 32 frequencies is divided
into two trains A & B of 16 frequencies. The inquiring device
4A initially transmits a series of inquiry packets each at a
different frequency taken from the train A. Each inquiry packet is
an ID packet of size 68 bits (68 .mu.s duration). Two inquiry
packets, at successive frequencies in the train A, are transmitted
in each even numbered slot. Thus a train of 16 inquiry packets is
transmitted over 10 ms. The train is then repeated at least 256
times. Then inquiry packets are repeatedly transmitted using the
remaining train B of 16 frequencies from the inquiry
frequency-hopping sequence.
[0019] Each connectable Bluetooth device that is available to join
a piconet 2 periodically enters an inquiry scan state in which it
scans for inquiry packets. During a scan a sliding correlator
correlates against the expected Access code and triggers when a
threshold is exceeded. In the inquiry scan state, the Access Code
used is derived from the Inquiry Access Code.
[0020] The Bluetooth Specification requires an inquiry scan to be
performed every 1.28 s or 2.56 s. The inquiry scan lasts between
11.25 and 2560 ms. During the inquiry scan, the receiver of the
Bluetooth device attempts sequentially to receive at each one of
the frequencies of the inquiry frequency-hopping sequence. The
phase within the sequence is determined by the Bluetooth Clock of
the connectable device. The receiving frequency typically changes
every 1.28 s.
[0021] If a connectable device 4C receives an inquiry packet during
the inquiry scan it will respond in an odd numbered time slot, by
transmitting a FHS packet which has the Inquiry Access Code as its
Access code and has, in its payload, the Bluetooth Device Address
and Bluetooth Clock value of the connectable device 4C.
[0022] An important consideration for Bluetooth devices is power
consumption. Typically, a Bluetooth device reduces power
consumption by remaining in a low power consumption idle state from
which it awakes periodically to enter the page scan state and/or to
enter the inquiry scan state in which power is consumed.
[0023] It would be desirable to further reduce power
consumption.
BRIEF DESCRIPTION OF THE INVENTION
[0024] According to one embodiment of the invention there is
provided a method of controlling a radio receiver comprising:
controlling the radio receiver for a first, relatively short,
period of time to detect radio transmissions in a predetermined
frequency band, and determining whether to control the radio
receiver for a subsequent second relatively longer period of time
to receive data from a subsequent radio transmission in the
predetermined frequency band.
[0025] There is an additional step of controlling the receiver for
a first, relatively short, period of time to detect radio
transmissions in a predetermined frequency band. This steps allows
the step of controlling the receiver for a subsequent second
relatively longer period of time to receive data from a subsequent
radio transmission in the predetermined frequency band to be
non-mandatory.
[0026] Thus a page san or inquiry scan need only be performed if
the radio transmissions detected in the first period of time
fulfill one or more predetermined conditions.
[0027] In the prior art, the page scan and inquiry scan were used
to obtain time and frequency synchronization and to receive data
(the Access Code) from the packet received during the scan. In
embodiments of the invention, the step of controlling the receiver
for a first, relatively short, period of time to detect radio
transmissions in a predetermined frequency band may enable the
receiver to obtain gross time and frequency synchronization. The
scanning step of controlling the receiver for a subsequent second
relatively longer period of time is used to receive data (the
Access Code) from a subsequent radio packet in the predetermined
frequency band. The gross time and frequency synchronization may be
used to initiate the scanning step at an optimal frequency.
[0028] According to another embodiment of the invention there is
provided a radio receiver device comprising: radio receiver
circuitry; a clock; and control circuitry for controlling the radio
receiver circuitry during a first, relatively short, period of time
to detect radio transmissions in a predetermined frequency band and
for controlling whether the radio receiver circuitry attempts,
during a subsequent second relatively longer period of time, to
receive data from a subsequent radio transmission in the
predetermined frequency band.
[0029] According to another embodiment of the invention there is
provided a chip-set for a radio receiver comprising: control
circuitry for controlling radio receiver circuitry during a first,
relatively short, period of time to detect radio transmissions in a
predetermined frequency band and for controlling whether the radio
receiver circuitry attempts, during a subsequent second relatively
longer period of time, to receive data from a subsequent radio
transmission in the predetermined frequency band.
[0030] According to another embodiment of the invention there is
provided a computer program comprising computer program
instructions which when loaded into a processor provide control
circuitry for controlling radio receiver circuitry during a first,
relatively short, period of time to detect radio transmissions in a
predetermined frequency band and for controlling whether the radio
receiver attempts, during a subsequent second relatively longer
period of time, to receive data from a subsequent radio
transmission in the predetermined frequency band.
[0031] According to another embodiment of the invention there is
provided a method of receiving data at a low power radio receiver
comprising: controlling the radio receiver to perform fast
frequency hopping for a first relatively short period of time to
detect radio transmissions in a predetermined frequency band, and
determining whether to control the radio receiver to receive for a
subsequent, second relatively longer period of time.
[0032] According to another embodiment of the invention there is
provided a method of controlling a radio receiver comprising:
controlling the radio receiver for a first, relatively short,
period of time to detect radio transmissions in a predetermined
frequency band and thereby obtain gross time and frequency
synchronization, and controlling the radio receiver for a
subsequent second relatively longer period of time to receive data
from a subsequent radio transmission in the predetermined frequency
band and thereby obtain exact time and frequency
synchronization.
[0033] According to another embodiment of the invention there is
provided a method of scanning in a low power radio receiver
comprising activating the receiver in a first mode in which the
receiver is periodically switched on for a relatively short period
of time to detect RF activity in a predetermined frequency band,
and, in response to detection of RF activity, activating the
receiver in a second mode in which the receiver is periodically
switched on for a relatively longer period of time to receive RF
signals in the frequency band.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] For a better understanding of the present invention
reference will now be made by way of example only to the
accompanying drawings in which:
[0035] FIG. 1 illustrates a Bluetooth piconet;
[0036] FIG. 2 illustrates a connectable Bluetooth device 4C that is
operable to perform conditional scanning;
[0037] FIG. 3A illustrates transmissions made in the ISM band when
the inquiring device 4A is performing the inquiry procedure;
[0038] FIG. 3B illustrates, using the same time axis as FIG. 3a,
the operation of receiving circuitry in a connectable device;
[0039] FIG. 4 schematically illustrates a chip-set for a radio
receiver; and
[0040] FIG. 5 schematically illustrates a computer readable medium
embodying a computer program.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0041] FIG. 2 illustrates a connectable Bluetooth device 4C that is
operable to perform conditional scanning.
[0042] It should be appreciated that although this device is
capable of joining and participating in a piconet 2 as a Slave it
may also be capable of separately forming a piconet in which it
would operate as Master.
[0043] The device 4C comprises radio transceiver circuitry 10
including radio receiver circuitry 11 and radio transmitter
circuitry 13; received signal strength indication (RSSI)
measurement circuitry 12 associated with the radio receiver
circuitry 11; a clock 14; control circuitry 16, which may be, for
example, a microprocessor and memory combination or a chip set; and
a user input interface 18. The control circuitry 16 receives an
input from the receiver circuitry 11 & RSSI measurement
circuitry 12, an input from the user interface 18 and an input from
the clock 14. The control circuitry 16 provides an output to the
transmitter circuitry 13.
[0044] FIG. 3A illustrates transmissions made in the ISM band when
the inquiring device 4A is performing the inquiry procedure. The
time axis extends from left to right. The inquiry device 4C
transmits a series of inquiry packets (ID packets) 21, 22, 23 . . .
26. Each inquiry packet 21-26 has a duration of 68 .mu.s and is
transmitted at a different frequency F1-F6. The frequencies used
are determined by the inquiry frequency-hopping sequence and lie
within the ISM frequency band. Pairs of inquiry packets are
transmitted in each of the even numbered slots 40, 42, 44. The odd
numbered slots 41, 43, 45 are used for reception by the inquiring
device 4A. The pairs of inquiry requests in a slot are separated by
half a slot (312.5 .mu.s). Thus the maximum separation between
adjacent inquiry packets in the series is 1.5 slots (937.5
.mu.s).
[0045] FIG. 3B illustrates, using the same time axis as FIG. 3a,
the operation of the receiving circuitry 11 in the connectable
device-4C. At time T1, the connectable device 4C begins to sniff
the ISM band and continues to sniff the ISM band until time T2. The
control circuitry 16 enables sniffing of the ISM band by
controlling the receiver circuitry 11 to detect radio transmissions
at each of the 79 channel frequencies in the ISM band.
[0046] The ISM frequency band (2402-2481 MHz) includes 79 Bluetooth
1 MHz channels. The connectable device 4C sequentially tries to
detect transmissions in each of the channels i.e. sniffs each of
the channels for transmissions. The inquiry packet has a duration
of 68 .mu.s.
[0047] In a preferred implementation, the connectable device
preferably sniffs each of the 79 frequency channels during a 68
.mu.s window. The receiving frequency at the connectable device 4C
therefore hops at 79/68 million hops per second. However, this
window may coincide with a period where the inquiring device 4A is
not transmitting. As the inquiring device 4A and the connectable
device 4C are not synchronized, the connectable device 4C has no
knowledge of if or when the inquiry packets are transmitted.
Therefore the cycling through of the 79 hop frequencies is repeated
a number of times between T1 and T2. In the example illustrated, it
is repeated 14 times, so that the first period of time has a
duration of 14*68 .mu.s i.e. 952 .mu.s. The first period of time is
thus greater than the maximum separation between adjacent inquiry
packets (937.5 .mu.s). The first period of time will consequently
coincide with one, possibly two, transmitted inquiry packets if an
inquiry procedure is on-going during the first period of time. In
the illustrated example, the radio receiver circuitry 11 will
detect a radio transmission corresponding to the inquiry packet 23
which is transmitted at frequency F3.
[0048] In other implementations, the connectable device preferably
sniffs each of the 79 frequency channels over a window greater than
68 .mu.s. The receiving frequency at the connectable device 4C may
therefore hop at less than 1 million hops per second. The cycling
through of the 79 hop frequencies is repeated a number of times
between T1 and T2 and the first period of time may have a duration
greater than 1 ms.
[0049] The radio receiver circuitry 11 detects a radio transmission
during the first period of time by using the RSSI measurement
circuitry 12. The RSSI measurement circuitry measures RSSI on the
currently sniffed channel and if the RSSI exceeds a threshold then
the RSSI measurement circuitry 12 informs the control circuitry 16.
The control circuitry 16 then records the channel frequency and the
current clock time. The recorded channel frequency and time provide
gross frequency and time synchronization which may be used to set
initial conditions for the receiver circuitry 11 if it is to be
used in a subsequent second period of time T3-T4.
[0050] Although RSSI detection is described other mechanisms for
measuring transmitted electromagnetic energy in the received radio
channel may be used.
[0051] The control circuitry 16 also controls whether the receiver
circuitry 11 attempts, during the subsequent second period of time
T3-T4, to perform an inquiry scan. The operation of the receiver
circuitry 11 during the second period of time is shown using dotted
lines as it is conditional i.e. depending upon circumstances the
receiver may or may not be used in the second period of time T3-T4
to perform an inquiry scan. Whether the receiver circuitry 11
performs an inquiry scan is dependent upon the results of the
transmission detection that has occurred during the first period of
time T1-T2.
[0052] If an inquiry scan is performed the connectable device 4C
attempts during the second period of time T3-T4, to receive an
Access Code of a transmitted inquiry packet. The second period of
time is between 11.25 ms and 2560 ms. As described previously a
sliding correlation window is used to detect the Access Code and
its detection establishes exact time and frequency synchronization
between the connectable device and the inquiring device. This
allows a packet to be subsequently sent from the connectable device
to the inquiring device. The frequency used at the receiver during
the inquiry scan is a slowly hopping sequence that hops every 1.28
s.
[0053] The condition(s) used for controlling the performance of the
inquiry scan may be positive or negative. A positive condition, if
fulfilled, enables the inquiry scan, whereas a negative condition
if fulfilled prevents the inquiry scan. Multiple conditions may be
used to control the inquiry scan but must always include a positive
condition.
[0054] One positive condition is `if any radio transmissions are
detected during the first period of time, then the inquiry scan is
performed`. If this condition is used by itself, then if no radio
transmissions are detected during the first period of time an
inquiry scan is not performed.
[0055] Another positive condition is `if any Bluetooth radio
transmissions are detected during the first period of time, then
the inquiry scan is performed`. If this condition is used by
itself, then if no Bluetooth radio transmissions are detected
during the first period of time an inquiry scan is not performed.
It may be assumed that a Bluetooth transmission has been detected
if there is only one or two radio transmissions detected during the
first period of time.
[0056] An example of a negative condition is `if any wideband
interference radio transmissions are detected during the first
period of time, then the inquiry scan is not performed`. If no
wideband interference radio transmissions are detected during the
first period of time, then an inquiry scan may be performed. A WLAN
network transmits in the ISM frequency band but has a channel
bandwidth of 20 MHz. The presence of such wideband interference
would result in multiple transmission detections over adjacent
frequency bands.
[0057] The sniffing of the ISM frequency band over the first period
of time is periodically repeated every 2.56 s and if the specified
condition(s), concerning detected transmissions during the first
period of time, are satisfied then the inquiry scan is performed
otherwise it is not performed.
[0058] The user interface 18 allows the connectable device 4C to be
manually switched between performing unconditional inquiry scanning
(as in the prior art) and conditional inquiry scanning as described
above.
[0059] The user interface 18 may also enable adjustment of one or
more of the first period of time, the speed of frequency hopping
during the first period of time, and the RSSI threshold used.
[0060] FIG. 4 schematically illustrates a chip-set for a radio
receiver that provides the control circuitry 16. The chip-set
comprises control circuitry for controlling receiver circuitry 11
during a first, relatively short, period of time T1-T2 to detect
radio transmissions in a predetermined ISM frequency band and for
controlling whether the receiver circuitry 11 attempts, during a
subsequent second relatively longer period of time T3-T4, to
receive data (Inquiry Access Code) from a subsequent radio
transmission 26 in the predetermined ISM frequency band.
[0061] FIG. 5 schematically illustrates a computer readable medium
embodying a computer program which when loaded into a processor
provides control circuitry controlling receiver circuitry 11 during
a first, relatively short, period of time T1-T2 to detect radio
transmissions in a predetermined ISM frequency band and for
controlling whether the receiver circuitry 11 attempts, during a
subsequent second relatively longer period of time T3-T4, to
receive data (inquiry access code) from a subsequent radio
transmission 26 in the predetermined ISM frequency band.
[0062] Although, FIG. 3 illustrates a series of inquiry packets
transmitted during an inquiry procedure, it will be realized from
the introduction that the Fig is also suitable for illustrating a
series of paging requests transmitted during the paging procedure.
The above description given in relation to conditional inquiry
scanning is also equally applicable to conditional page
scanning.
[0063] The information concerning the frequency of the radio
transmission(s) detected during the first period of time and the
time of the detection can be used to set the initial conditions for
the subsequent inquiry scan or page scan.
[0064] For an inquiry scan, for example, it is assumed that the
detected packet 23 is an inquiry packet sent at a frequency from an
inquiry frequency-hopping sequence derived from the General Inquiry
Access Code (GIAC). The recorded frequency of detection F3 is used
to determine the phase of the inquiring device within the sequence
at the time of detection. The phase of the inquiring device within
the sequence at a future time e.g. T3 can be determined from the
recorded time of detection and hence the frequency of transmission
F4 used by the inquiring device at the future time T3 can be
determined. Thus an inquiry scan can be initiated at the determined
frequency F4 at that future time T3.
[0065] For a page scan, for example, it is assumed that the
detected packet 23 is an page request sent at a frequency from the
page frequency-hopping sequence derived from the Bluetooth Device
Address of the connectable device. The recorded frequency of
detection F3 is used to determine the phase of the paging device
within the sequence at the time of detection. The phase of the
paging device within the sequence at a future time T3 can be
determined from the recorded time of detection and hence the
frequency of transmission F4 used by the paging device at the
future time T3 can be determined. Thus a page scan can be initiated
at the determined frequency F4 at that future time T3.
[0066] Alternatively, for an inquiry scan, it is assumed that the
detected packet is an inquiry packet sent at a frequency from an
inquiry frequency-hopping sequence derived from the General Inquiry
Access Code (GIAC). The recorded frequency of detection is used to
determine whether the inquiring device is using train A or train B.
An inquiry scan can be initiated using the determined train of
frequencies.
[0067] Without the use of this invention, a Bluetooth device in
idle state turns on its transceiver circuitry 10 to perform a page
scan and an inquiry scan every 1.28 or 2.56 seconds. The page scan
and the inquiry scan each last a minimum of 11.25 ms. Therefore the
transceiver is switched on twice for a minimum of 11.25 ms every
2.56 seconds. That is the radio transceiver 10 is on for a minimum
of 0.88% of the time. By contrast, in the described embodiment of
the invention sniffing occurs for 938 .mu.s every 1.28 or 2.56
seconds. This corresponds to the transceiver being on for 0.037% of
the time. This corresponds to a 96% reduction in transceiver
circuitry on-time.
[0068] Although embodiments of the present invention have been
described in the preceding paragraphs with reference to various
examples, it should be appreciated that modifications to the
examples given can be made without departing from the scope of the
invention as claimed. For example, although the invention has been
described in relation to Bluetooth it may have application in other
radio communication technologies.
[0069] Whilst endeavoring in the foregoing specification to draw
attention to those features of the invention believed to be of
particular importance it should be understood that the Applicant
claims protection in respect of any patentable feature or
combination of features hereinbefore referred to and/or shown in
the drawings whether or not particular emphasis has been placed
thereon.
* * * * *